(1) Field of the Invention
The present invention relates to a seal arrangement for use in gas turbine engines, and more particularly to a tandem dual element seal used in the seal arrangement.
(2) Prior Art
Carbon seals have been the bearing compartment primary seal of choice in engines for many years. Segmented circumferential carbon (SCC) seals have been used in recent engines based upon their low air consumption and their ability to accommodate large relative motion in the axial direction. This sealing system consists of static components, the carbons, which are contained within a metallic housing—typically constructed of titanium or steel. The rotating component that comprises the other half of the sealing system is referred to as the seal runner. Air pressure and circumferential springs compress the static carbons against the rotating seal runner to keep the oil contained within the bearing compartment.
Referring now to FIG. 1, one approach for isolating one cavity 10 from a second cavity 12 involves the use of a single element carbon ring seal 14 on each rotating shaft. The carbon ring seal 14 separates the buffer gas cavity 10 from the cavity 12 in the bearing compartment. Adequate pressure is maintained in the cavity 10 by use of a labyrinth seal 16, which is placed between the cavity 10 and the cavity 18 to backpressure the buffer gas. There are shortcomings using this approach. For example, the approach is subject to a lack of gap control between cavity 10 and the cavity 18 via the labyrinth seal 16, which results in varying back pressure and varying seal delta P (ΔP). Increasing the labyrinth seal gap, to accommodate maneuver deflections, reduces the buffer gas pressure, thereby reducing the delta P across the carbon seals. The changes in pressure in the cavity 18 greatly influences pressure in the cavity 10 and therefore the seal delta P.
Another deficiency of the prior art seal arrangements is that they are dependent upon other features, such as labyrinths, in order to seal the bearing compartment.